A density functional study of neutral and anionic vanadium trimer monoxides is presented. The calculations were of all-electron type employing a newly developed basis set for the vanadium atom. Different isomers of V3O and V3O- were studied in order to determine the ground state structures. For both systems a planar C-2v structure with an edge-bonded oxygen atom was found as the ground state. Equilibrium structure parameters of ground states as well as low-lying excited states, harmonic frequencies, the adiabatic electron affinity, and Kohn-Sham orbital diagrams are reported. The experimental negative ion photoelectron spectra of V3O was simulated by calculating multidimensional Franck-Condon factors, using the geometries and harmonic frequencies of the calculated ground states of V3O- and V3O. The good agreement between the experimental and the theoretical spectra allows the determination of the ground state structure of V3O and V3O-. This represents the first work in which a simulation of a vibrationally resolved negative ion photoelectron spectra of a transition metal oxide is presented. (C) 2003 American Institute of Physics.